Telephone system



Dec. 27, 1938. J BAUMFALK TELEPHONE SYSTEM Filed Oct" 1e, 1935 e Sfiets-Shet 1 M mm o To U i MW Nu U rm W m Q. J

A T TORNE V J. BAUMFALK Dec. 27, 1938.

TELEPHONE SYSTEM Fil ed Oct. 16, 1935 s Sheets-Sheet 2 n QMNQQ QL mwm lNl/ENTOR J BAUMFALK I TTOR/Vft I BAUMFAI-K 2,141,372 TELEPHONE SYSTEM Filed Oct. 16, 1955 e Sheets-Skeet 3 ATTORNEY- J. 'BAUMFALK TELEPHONE SYSTEM Filed obi. 16, 1955 6 Sheets-Sheet 4 v lNl/ENTOR J. BAUMFALK ATTORNEY Dec. 27, .1938. t Y J. BAUMFALK 2,141,372

TELEPHONE SYSTEM Filed Oct. 16, 1955 e Sheets-Sheet 5 POLARIZED INVENTOR J. BAUMl-XLK I. WWM

ATTORNEY Dec. 27, 1938. Y J. BAUMFALK- TELEPHONE SY STEM File d Oct. 16, 1955 e Sheets-Sheet s INVENTOR J. BAUMFZLK A T TORNE V Patented Dec. 27, 1938 UNITED STATES LMLE? PATENT owner I 2,141,372 TELEPHONE SYSTEM Application October 16, 1935, Serial No. 45,185

26 Claims.

This invention relates to telephone systems and particularly to systems involving circuits for transmitting and repeating operating and supervisory current impulses.

The objects of the invention are to extend the operating range of trunk lines, arranged for completing calls in either direction, by the use of a novel impulse repeating mechanism; to enable the use of a single repeating mechanism for the outward calls originating in each of a plurality of branches of said trunk; to enable the use of said repeater for all outward calls originating as just noted and also for all calls incoming over said trunk in the other direction; to improve the transmission of both switch operating and super- Visory impulses by converting all direct current pulses into corrected alternating current pulses for transmission over the trunk line; to facilitate the passing of supervisory signals from one exchange to another by converting the alternating supervisory currents into either reversals of direct current or direct currents with open and closed periods according to the source from which the call originated; and to improve otherwise the efficiency and effectiveness of systems of the kind herein described.

Repeating mechanisms have been devised heretofore for repeating impulses in either direction over a transmission line. It is also old tocorrect the repeated impulses when transmitted in one direction. Other systems have been proposed in which alternating current is used for sending both switch operating and supervisory signals over trunk lines in either direction.

According to the present invention, however, a two-way trunk line is provided with a branch for originating outward calls and a second branch for receiving calls incoming over said trunk together with a repeater arranged to have its input circuit associated either with said first mentioned branch or said trunk and its output circuit either with said trunk or said second branch, according to the direction of the call.

Another feature is an arrangement in which either of two call originating circuits, one for manual calls and the other for automatic calls, may be connected to the trunk outgoing to the distant office, whereas calls coming over the trunk and then sent over the trunk to the distant ofiice Where they are converted into another form and applied to either the manual or the automatic call originating circuit depending on which one is involved in the connection. If the call was extended from the manual circuit, the incoming alternating supervisory signals are converted into signals of direct current with open and closed circuit periods to operate a lamp at an operator's position. If on the other hand it was extended from the automatic branch, the incoming signals are converted into reversals of direct current to cause the well-known supervisory effects in the automatic circuits.

Another feature is an impulse repeater having a single input and a single output circuit so arranged that the impulses which represent the call, whether incoming or outgoing over the trunk line, are delivered to said input circuit and the repeated impulses in said output circuit are, according to the direction of the call, either delivered to the trunk for transmission outward to the distant office or to the switches on the incoming end of the trunk in the case of an inward call, together with means whereby all impulses delivered to the repeater are corrected thereby regardless of the direction of the call.

Another feature of this invention is a supervi sory signal arrangement wherein a series of signals are repeated from one circuit to another in such a way that the repeated signals in the outgoing circuit are sent in synchronism with the originating signals in the incoming circuit until the rate of the incoming signals passes a certain frequency. Beyond this frequency value the frequency of the outgoing signals remains fixed, but before each outgoing signal is sent the incoming circuit is tested to determine whether its condition 7 claims.

A better understanding of the invention may be had by reference to the accompanying drawings, in which:

Figs. 2 and 3 illustrate diagrammatically a system involving a plurality of exchanges, such as private branch exchanges, together with interconnecting two-way trunk lines; and

Figs. 4, 5, 6 and '7, when taken in the order 7 indicated in Fig. 1, disclose,'partly in detail and in part diagrammatically, the equipment located at one of the exchanges. Fig. 4 shows a calling. subscriber's station, a line finder switch, a. first selector switch and one branch of the outgoing two-way trunk. Fig. 5 shows an attendant operators dial and cord circuit and a second branch 7 of the trunk over which calls may be originated.

This figure also illustrates 2. called subscribers.

line and selector and connector switches for extending to said line calls incoming over the twoway trunk. Figs. 6 and '7 show the outgoing conductors of the trunk, which extend from the distant exchange, and the repeating and controlling mechanism for use in connection with both outgoing and incoming calls.

The subscribers stations are provided with the usual telephone sets and with dials for controlling the establishment of the desired connections.

The line finder, selector and connector switches may be of any well-known type-such as the step-by-step strowgeriswitch. Switches of this type are described in pages 53 to 67, inclusive, of the second edition of Automatic Telephony by Smith and Campbell.

Referring first to Figs. 2 and 3; which show the 7 system as a whole, any'two exchanges in the systern, such as exchanges P. B. X. i and P, B. X 2, are interconnected by a two-way trunk T. Galling stations, such as station A in exchange P. B. X.

i, may complete calls in the usual manner to other stations in the same exchange or may ex-' tend a connection to a distant exchange, P. B. X. 2. To make a distant call, the connection is extended over line finder LF, selectorSl and] thence over the two-way trunk oiruit T to the exchange P. B. X. 2, thence over an incoming selector S4 and a connector CI to thecalled station, such as station BI. On the other hand, stations in the exchan e P. B. X. i may obtain calls with the assistance of the attendant. In this case the attendant dials for the called station, and aconnection is completed by way of her cord circuit 534, jack 543 and thence over the trunk as above described. All incoming calls from a distant exchange by way of the trunk T are completedin the exchange P, B. X. l by way of incomingselector S2 and connector C. The foregoing explanation also applies to exchange P. 'B. X. 2. In addition to calls from one exchange to another, a station in any exchange may make calls to distant exchanges byway of one or more intermediateexchanges. For example,"station A may obtain a connection over trunk T through selectors S t and S5 in exchange P. B. X. 2' and thence over trunk Tl, which is similar to trunk T,-to a third exchange and by. way of switches therein to the called station. I 1

In all of the connections completed over trunk T in either direction the dial and supervisory impulses are transmitted'ov'er thetrunk by means of alternating current. At the originating exchange the direct current dial and supervisory signals are converted into alternating current signals for transmission over the trunk, and at the incoming end of the trunk in the distant exchange these signals are again converted into direct current signals. The dial impulses are repeated at the outgoing end by means of a repeating mechanism that serves not only to convert the impulses from direct current into alternating current but also to correct them for fast and slow dials.' The same repeating mechanism serves onincoming calls to receive the incoming alternating current dial impulses and to convert them into direct current impulses for operating the local switches.

' Since the equipment located in one exchange is similar to that in each of the other exchanges, the detailed disclosure inFigs. 4 to- '7 has been limited to a single exchange. It is assumed that the equipment in these figures is located at exchange P. B. X. l, and it will be understood that the equipment at exchange P. B. X. 2 at the other end of the two-way trunk T is identical with that shown in detail in Figs, 4 to 7.

While the exchanges interconnected by the two-Way trunks are referred to herein as private branch exchanges, the invention is not so limited but may be applied to systems involving other kinds of exchanges and oflices.

Outgoing call from dial station 'hunts' for and extends the line I through its brushes 2 to the first selector Si. When the calling subscriber dials the first digit of the called subscribers number, the brushes 3 of selector switch SI are advanced to the corresponding group of terminals; The selector S! then automatically hunts for and seizes an idle 'set of outer back contact of relay 4! l, conductor M5,

the lower winding of relay 4|! to ground through the lower winding of relay M8. Relays 4H and M8 become energized over this loop circuit. Operation of relay 4!! establishes .a circuit from ground through'the upper front contact of relay ii! to battery through the winding of relay M9 thereby causing relay M9 to become energized.

Operation of relay 4 l 9 closes a circuit from ground through the upper outer front contact of relay M9 to the sleeve terminal 410 of the selector SI to make the selected set of terminals test busy to other selectors and to hold the preceding switches. Ground is supplied also through the upper inner front contact of relay M9, overconductorAEi to battery through thewinding-of relay 5%. Relay MEenergiZed, furnishes battery'from the upper inner front contactof relay 545 through resistance 54! to ground through the filament of lamp 548 causing lamp 548 to light as a busy signal to the-operator at the multiple jack 543 and the multiples thereof. Ground is furnished also through the upper outer front contact of relay 7 545 to the sleeve terminal of jack 543 as a busy condition. Ground through the lower front contact of relay 545 is furnished over conductor 540 to battery through the winding of relay 621 which operates and furnishes off-normal ground to the trunk circuit. Opening the lower outer back contact of relay 4|9 opens the circuit through relays M3 and 590 in order to prevent mutilation of a call if the operator should plug into either jack 509 or jack 543 over the busy signal. Operation of relay 4]! also establishes a circuit from ground through the right back contact of relay 6i5, conductor I41, the upper inner back contact of relay H9, the upper back contact of relay H8, conductor 444, the lower front contact of relay 4H, conductor 436, the upper back contact of slow-to-operate and slowto-release relay 629, conductor 440, the windings of relays 623 and 624 in parallel, the lower back contact of relay 636 to battery thereby causing 1 relays 623 and 624 to become energized. At the same time, the ground from the right back con tact of relay 6l5 which was closed to conductor 435 in the manner outlined heretofore is extended from conductor 436 through the upper outer back contact of relay H9, conductor (48, to battery through the winding of slow-to-operate and slowto-release relay 625. operate, permits relays 623 and 624 to operate before the upper back contact of relay 629 is broken.

Operation of relay M8 closes a circuit from ground on conductor 444 supplied from the right back contact of relay 6I5 as previously described, through the lower front contact of relay M8, conductor 458 to battery'through the winding of slow-to-release relay 5H4 causing relay M4 to become energized. Operation of relay M8 also completes a circuit from ground on the upper back contact of relay I05, through the upper back contact of relay I29, conductor 454, the upper front contact of relay 4l8, conductor 442, the lower back contact of relay I64 to battery through the winding of relay M4. Relay N34 is energized and locks in a circuit through resistance I l to the operating ground on conductor 442. Operation of relay lM'closes a circuit from ground through its upper frontcontact, conductor 540 to battery through the winding of relay 621. Operation of relay I54 also removes the short circuit from around resistance H0 placing resistance H0 in series with the winding of relay H14 in order to reduce the current drain. Relay 62! being energized furnishes a ground through its upper inner front contact, conductor 15I, the upper back contact of relay I22, winding of relay I65, the lower front contact of relay 164, resistance Jill, winding of relay I04 to battery. Relay I does not operate at this time because it is shortcircuited by the operating ground for relay I04 which ground was previously traced to the lower armature of relay I54.

Relay 52'! operated, also places a bias on polarized relay 122 over a circuit extending from ground through the upper inner front contact of relay 52?, conductor 15!, the lower back contact of relay H35, the upper back contact of relay E20 to battery through the upper winding of polarized relay E22 thereby preventing the operation of polarized relay 122. The ground on conductor l5l Relay 629, being slow to.

relay 606. Relays I06 and 606 become energized. 7

Relay 606 energized removes the short circuits from certain of the windings of the repeater 660 by opening the back contacts of relay 606. Polarized relay Hi6 operated, establishes a circuit from ground through the upper inner front contact of relay 621, conductor 15! to the upper end of the winding of relay 101, and through the upper front contact of polarized relay 106 to the lower end of the winding of relay thereby short-circuiting relay 10! and preventing the operation of relay I01, and through the lower back contact of relay 151' to battery through the upper winding of relay I24. Relay I24 operated places a short circuit around resistance I23. Relay 62! operated also prepares a circuit from battery, winding of relay 626, lower front contact of relay 62'', conductor I56 to the upper back contact of polarized relay 166 so that relay 626 will operate when the circuit is closed to ground on conductor ml by the release of polarized relay I05.

Operation of slow-to-release relay 5! 4 closes a circuit from ground through the lower inner front contact of relay 5|4, conductor 512 to battery through the winding of slow-to-release relay IOI which now operates. Relay T0! operated closes a circuit from ground furnished on conductor 444 from the right back contact of relay H5 in a manner previously described herein through the upper outer front contact of relay 514, conductor 51!], the upper outer front contact of relay HM, conductor 139 to battery through the winding of relay 63L Relay B3l is thus energized,

Operation of relay 5l4 also closes a circuit from ground on the right back contact of relay 5E5, conductor Ml, the upper inner back contact of relay H9, the upper back contact of relay H8,

of relay 5l4 furnishes a ground over conductor 51!, the upper outer front contact of relay 829 to conductor 436 thereby supplementing the ground supplied from the right back contact of relay M5 to conductor 435 as described heretofore. The ground from the upper inner front contact of relay 5E4 is also extended from conductor 436 through the upper outer back contact of relay H9 to battery through the winding of relay 529 thereby holding relay 625 operated after the seizure pulse is completed. Ground is also supplied through the lower front contact of relay 514 over conductor 455 to sleeve terminal 465 of the selector SI as a busy condition.

Relay 623 operated, connects the conductors 676 and 57! through the inner front contacts of relay 623, windings of retard coil [N53, to the right winding of the transformer 5l8. Induction from the left winding of transformer 8E8 connected to the source of alternating current supply til thereby supplies alternating current to the line as a signal to the distant exchange P. B. X. 2. Relay 524 operated closes circuits from conductors 6N! and 6', through condensers 512 and 613 to of relays E523 and 52 i.

ground through the upper front contact and the lower inner front contact of relay 624 in order to prevent acoustic'shocks. Relay 624, operated, also closes a circuit from ground through the lower outer front contact of relay 624i, conductor 7.

13 2, to battery through the Winding of relay 66! thereby causing relay 60] to become energized; Operation of relay 6!]! closes a circuit from ground through the left outer front contact of relay till, conductor 33! to batterythrough the Winding of relay 425 causing. relay 425 to become energized. Relay EDI operated, also closes a circuit from ground through the left inner front contact of relay 69! to battery through the winding of relay 621. Relay 627 is held energized.

After a predetermined interval has elapsed after the operation 'of the'relay an the slow-to-operate relay E229 operates and opens the operating circuit for relays 523 and 524 through the upper back contact of relay 629 and thus permits the release Release of relay 623 disconnects the alternating current from the conductors tit! and 6H and terminates the seizure signal. Relay 62 3 released removes the ground from condensers 6'52 and B13 and opens the circuit to the winding of .relay 69! which in turn releases and removes the ground from conductor 13i permitting the release of relay 425. Operation of relay 629 establishes a circuit from battery, through resistance MI, in parallel circuit with resistance 422 and winding of relay A29, the upper back contact'o'f relay 42B, conductor ii-ll, the upper inner front contact of relay SEQQQconductor M5, the upper back contact of relay 126,

conductor M5 to the right front contact of relay 655 for supervisory purposes which will :be ex plained hereinafter. -Also, operation of relay 6251 establishes a circuit from. ground through the upper inner front contact of relay '52'5, conductor i315, the lower front. contact of relay '529, the upper outer backcontact of relay Hi3, conductor rat, the lower back contact of relay 626, conductor F55, the upper inner back contact of relay m3, conductor M9 to battery'through the winding of relay 62B. Relay 628 is energized. Relay 62% holds under control of relayttl;

Relay 63! ground over conductor 139 to the sleeve terminal MD of selector SI, provides an auxiliary holding path for relay 529, holds relay 4 28 and provides an operating path for relays 623 and $26 when relay 4 It releases on pulsing or'disconnect;

Calling station dials winding of relay 785, the upper back contact of relay T22, conductor 75l toground through the upper inner front contact of relay, 62?. Relay 1% holds operated over this same circuit. M8 released, also closes a circuit for the operation of relays623 and 624. This circuit extends from battery through the lower back contact of relay 638, windings of relays 623 and 624 in parallel, conductor 449, contact 594 of relay 593, conductor 513, the lower outer front contact of relay operated, connects an auxiliary,

Relay 63!, conductor'M3, the lower back Contact of 'which opposes the upper winding of relay 796 causing relay 7% to release, and removesthe ground from the biasing circuit which has previously been traced through the lower winding of relayl22, When off-normal ground through the'lower back contact of relay IE5 is removed,

. condenser 163 which has been discharged by this ground now charges in a circuit from battery through the upper win-ding of relay 122 to ground through condenser E63 and resistance 62. Current will continue to flow through the upper winding of relay 522 during the charging of cone lay l2t to' operate in acircuit, extending from the upper inner front contact of relay 62?, conductor 75L the lower front contact of relay we, the winding of relay l2fl and resistance TZI in parallel, to: battery through resistance T25. When relay 186 releases the upper front contact 'of relay 7% is opened and the short circuit around the Winding of relay H1! is removed. Relay l9? opcrates in a circuit extending from ground on the upper inner front contact of relayllizl, conductor 75E; winding of relay'lfll, to battery through resistance 109. Closure of the upper back contact of relay tilt establishes a circuit from ground on the upper inner front contact of relayv 621, conductor i5l, upper back contact of relay 5%, conductor 756, lower front contact of relay 621, to battery through the winding of relay 626. Relay 62% operates. Operation of relay 7!]? opens the circuit through the upper winding of relay i2 1. Relay F24 remains operated in a circuit from battery through its lower winding and its lower front contact in parallel with resistance T25 and in series with the Winding of relay 125 and resistance 'l2l to ground on the upper inner front contact of relay 621love!" the circuit previously traced. Relay Fill operated also opens the circuit previously traced from off-normal ground on the upperinner front contact of relay 621, to the winding'of relay 8GB permitting relay 656 to release. ;Relay ll)? operated, also closes a circuit from olf-normal. ground on the upper inner front contact of relay 627, conductor the upper front contact of relay 167, contact N2 of relay H5, conductor 5373, contact 594 of relay 590, conductor 449, windings of relays 623and 62 4 in parallel, to battery through the lower back contact of relay 63B thereby holding relays 623 and 524 operated. Relay'62fi operated causes relay 5%? to operate over acircuit previously described. Re-' lay 6M operated causes relay 325 to operate over a circuit previously described. Relay Elli operlower left windings of repeating coil 6M. Relay.

$25 operated opens the circuit to terminal 468 and connects the upper end of the Winding of resistance 421 through the front contact of relay 425, the upper front contact of relay 428, to conductor Q32, thereby connecting the resistance 42'! across the upper left and the lower left terminals of repeating coil 6M. Relay 666 released shortcircuits the telephone repeater 666. Relay 623 operated connects the line to the armatures of relay 626. Relay 624 operate-d connects condensers 672 and 613 to ground in the manner previously described. Relay 12E! operated opens the circuit through its lower back contact to the resistance HI thereby removing the shunting resistance H I from around the winding of relay 165.

When the relay E22 operates it opens its upper back contact and thus opens the holding circuit previously described for relays TM and 765 permitting these relays to release. Relay I64 released short-circuits. resistance H through the lower back contact of relay Hi4. Relay I released reconnects the ground on the upper back contact of relay 565 to the armature of relay M8 over a circuit previously described, and removes the ground from the lower winding of relay 166. This ground has previously discharged condenser F66. Now when the ground is removed, condenser H66 charges in a circuit from battery through the lower winding of relay 166 to ground through condenser Hi6 and resistance 16L Current will continue to flow through the lower winding of relay 706 during the charging of condenser l'fifl and the ampere turns'producecl by the charging current in the lower winding of relay H16 oppose the ampere turns in the upper winding of relay :66. As the condenser 1656 becomes charged the ampere turns in the lower winding of relay i116 decrease and the relay T66 is caused to operate by the ampere turns in the upper winding of relay M6 in a manner Well known to the art. Relay 765 released also opens the hold ing circuit previously described for relays 120 and 32d, and the holding circuit previously described for relay 62!) since relay 626 is now oper v ated. Relay 626 released connects alternating current to the line through its back contacts in the manner described hereinbefore. The relay 124 released removes the short circuit from resistance 723. The relay T20 released closes a circuit from ground on the upper inner front contact of relay 621 over conductor 15!, the lower back contact of relay 120, resistances H l and I I0 to battery through the winding, of relay 104 which does not energize relay 164 sufliciently to cause it to operate but sufficiently to cause relay 104 to operate quickly when relay H6 is operated on the next dial pulse. Relay 120 released also closes a circuit from ground on the upper inner front contact of relay 621 over conductor Hi, the lower back contact of relay 105, the upper back contact of relay 120 to battery through the upper winding of relay 122 causing'relay 122 to release and close its back contact.

Let us assume that the dial at station A has a speed in excess of the average speed of such dials. Relay M8 reoperates on the succeeding closure of the loop circuit through station A and causes relay Hi l to reoperate over a circuit previously described. Relay M8 releases on the succeeding open period of the dial pulse and permits relay 135 to reoperate over a circuit previously described. Relay ms operated closes the circuit through the lower winding of relay 106 beforethe upperwinding of relay 166 overcomes the lower winding,'thereby preventing the operation of relay I06. Relay Hi5 operated also causes relay 620 to operate over a circuit previously described thereby disconnecting the alternating current from the line and terminating the previous pulse. Thus on high dial speeds the period between pulses during which alternating current is connected to the line is determined by the operating time of therelay 122 minus the operate time of relay 620 plus the release time of the relays 105 and 626 regardless of the per cent break of the pulses received.

Letv us assume that the dial at the calling station A has a speed below the average. Relay H8 reoperates on the succeeding closure of the loop circuit through station A and causes relay IM to reoperate over a circuit previously described. However, before the relay M8 releases on the succeeding open period of, the pulse to permit the operation ofrelay H35 which closes.

the circuit through the lower winding of relay 106' the upper winding of relay 166 is energized in a circuit previously described and relay 166 operates. Operation of relay 166 opens the holding circuitpreviously described for relay 626 permitting relay 626 to release and release therelay 626 which in turn releases and connects the alternating current to the line as described hereinbefore sending a pulse to the distant ofiice. Thus, on slow dial speeds, the period between pulses during which no alternating current is connected tothe line is determined by the operate time of relays I06 and 620 plus the release time of relay 626 minus the release time of relay 626 regardless of the percentage break of the pulses received. The relay 166 operated also short-circuits the winding of relay 101 but relay I66 reoperates on'the next-pulse before relay it! has time to release. The condenser 622 and the resistance 62l are bridged about the winding of relay 62!) in order to improve pulsing.

On single pulse digits or on the last pulse of other digits, the period of the pulse during which no alternating current is connected to the line is thesame as on slow dial speeds regardless of the speed of the pulsing received. In this case, the relay 166 operated, short-circuits the winding of relay I01, causing relay 107 to release and in turn operatethe relays 606 and 124 and release the relays 623 andv 624 over circuits previously described. Relay 623 released, reconnects the conductors 610 and 6' to the right windings of repeating coil 661. Relay 624 released, releases relay 60 l and disconnects ground from condensers 612 and 613 in the manner previously described. Relay 60! released removes the short circuits from the left windings of repeating coil 666 and releases relay 425. Relay 425 being slow-to-release prevents acoustic 'shocksto the originating party before reestablishing the talking circuit. Relay 606 operated removes the short circuits from the telephone repeater 660. Relay 124 operated shortcircuits the resistance 123. The relay I24 being operatedduring the operating time of the relay 122 on the first pulse of each digit increases the current in the lower winding of relay 122, thereby making relay 122 faster to operate so as to compensate for the fact that the relays delivering pulses to this circuit are slower to release on the first pulse of a digit than on succeeding pulses.

V Called subscriber answers received over the loop established from conductor 610 through the upper right winding of repeating coil 60?, resistance 60 9, copper oxide rectifiers. (H0, 0|2 and 6|3, the left winding of,

relay |5, the lower winding. of repeating coil 501 to conductor 61!. The manner in which thisanswering supervisory pulse is sent from. the" distant end will be described hereinafter in connection with an incoming call. Relay |i|5 operates on the rectified current and. establishes a circuit from ground through the right front'contact of relay 6|5, over conductor 146, the upper back contact of relay 726, conductor 145,. the upper inner front contact of relay 629,. conductor 43], the upper back contact of relay 420,.=w inding of relay 420, to battery through resistance 422. Relay 420operated locks in a circuit extendingv from battery through resistance 422, the winding of relay 420 the upper front'contactof. relay'flli to ground through the upper inner front contactof relay M9. At the end'of the supervision pulse, relay 6 5 releases on the open circuit and removes the short circuit from the winding of relay 4 H. Relay 4 operates in'a circuit extending from; battery through resistance 4'2l, winding of relay Al the upper front contact of relay 420 toground art, such as message register controlor operators supervision. The circuit is now ready for talking.

During talking, relays 4H,. M1, 418, 4|9,.420,. 428,

SM, 545, 605, 620,621,. 529, 63L. 104:, Miami;

places a short circuit through the lower front contact of relay 4| around the winding of relay' '420.

circuit described for relay 4H. Relay 4, how

Relay 420 releases and opens; the holding ever, remains operated through the upper back contact of relay 420' to the ground supplied from the front contact of the relay til-'5. When the pulseof alternating current: from the distant private branch exchange terminates; relay 4:: releases and again reverses the battery and ground to the originating end. If the called party removes his receiver again before the originating end disconnects, alternating current will be connected again to the conductors 610:- and 6H, and the relays 615, 4| and 420 will. operate in the manner described heretofore.

If the calling party A disconnects first, relays 5|! and M8 release on open circuit. Relay 4|] released, releases relay (9. Relay 41:8;released, releases relay 5M and operatesrelay's 623 and 624 in a circuit previously traced herein. Relay 4-18 released, removes the short circuit around the winding of relay 105. Relay 6'23 operateddisconnects the conductors 610 and 6H- from the repeating coil 5G1. Relay 624 operated, operates relay 60! which in turn operates relay 425 as described heretofore. When the short. circuit is removedfrom relay 105 bythe release: of relay M0, the relay 105 operates in series. with resistance H0 and the winding of relay I04. Relay 7'05 operated holds the relay 620? operated to ground. on the upper inner front contact of relay sleeve. terminal 4100f the selector SI.

which. in turn releases relays 425 and. 627.

621 over a. circuit previously. described, releases relay 105: by applying ground to the lower wind-.

relay l22' operates, relays 704 and 105 release.

Relay I05 released, releases. relays 122, 120' and 620, holds. relay 626 operated over a circuit ineluding the upper contact of relay 626 and normal: contacts of relays M8 and T29, and again permits relay 106. to operatein the manner described heretofore. Relay 620 released connects 1 conductors 610 and. 6' to the alternating current source in the manner. described heretofore as a disconnect signal to the distant private branch. exchange. Relay I05 operated, releases relay E07. Relay 5|4 released, releases relay 10L Relay i01 released, releasesrelays '63l, 4| l, 420 and 545. Relay 63| released, releases relays 428, 523', 524 and 629, and removes ground from. the Relay 02-3 released, terminates the alternating current pulse that is sent to the distant private branch exchange. Relay 624 released, releases relay 61H;

RelayfB-Z'I: released, releases relays 625, 106 and E24, removes ground from the sleeve of. the selector Si and thereby restores the circuit to normal.

Outgoing call from attendant. to distant exchange Wheira subscriber desires a private branch exchange attendant to complete a call over this trunk, he dials for theattend-ant in the usual manner. Thefattendant inserts the plug 533 of the cord 534 into the calling jack 529'and obtains the number desired by the calling subscriber and inserts the plug 505 of the dial cord associated with the dial 500' into the dial jack509 associated with the trunk circuit. Also, the attendant inserts. the plug 535 associated with the cord 534 into the talking jack 543 associated with the trunkcircuit; The trunk circuit is so: arranged that a cord may be connected to either the dial jack 509 or the talk jack 543 first. Assuming that the attendant plugs into the dial jack 509 first, relay 513- operates ina circuit extending from ground through the windingof relay 50| in the attendants'= dialing cord, the sleeve of plug 505- and the sleeve of jack -9; the winding of relay 5|3, conductor 4-55, the lower back contact of relay M9,. conductor 452. the lower back contact' of relay H5 to battery through resistance N1. No other relays operate until the plug 505 is fully seated in jack 509. When the plug 505 is fully seated in the 'jack 509, relay 5H operates in series with relay M8 in a circuit extending from ground through the lower winding of relay 418, conductor 453, the upper outer front contact of relay 5| 3-, the tip conductor of jack 509, the tip conductor of plug 505, the loop circuit through the dial 500, the ring conductor of plug 505, the ring conductor of jack 509, winding of relay 5, the upper inner front contact of relay 5| 3,. conductor 456 to battery through the upper winding of relay il-8. Relay 5 operated, operates relay 5|2 in a. circuit extending from ground through the lower front contact of relay 5 to battery through the winding of relay 5|2; Relay 5|? operates and locks ina circuit extending from: battery through the winding of relay 5. Relay 5 releases. Relay 5l2'operated, also closes a circuit from ground through the lower outer front contact of relay 5E2 through the winding of relay 5%, conductor 455, the lower back. contact of relay M9, conductor 552, the lower outer back contact of relay H6 to battery through resistance ll'l. Relay 590 operated, connects ground to the sleeve terminal MB of the selector Si in a circuit extending from ground through contact 553 of relay 596, conductor 466' to sleeve terminal M5 of selector Si as a busy condition. Relay 590 operated also transfers the trunk from the incoming selector S2 to the tip and the ring conductors of the talk jack 553. Relay il8 operates over the circuit previously traced for the operation of relay 5H. The relay 428 does not operate on this type of call since the operating path for relay' i28 is open at the lower inner back contact of relay 596. After relay M8 operates, the circuit functions as described heretofore in the description of a call being completed from a subscriber at substation A and prepares the tie line circuit in the distant private branch exchange for receiving dial pulses. The circuit is now ready for dialing.

Assume that the attendant inserts the plug 535 of the cord 534 into the talk jack 543 before she inserts the plug 505 of the dialing cord. into the dialing jack 569. Relay 59!] operates in a circuit extending from ground through the make contact of talk jack 543, winding of relay 595, conductor 455, the lower back contact of relay 4 l 9, conductor 452, the lower outer back contact of relay H6 to battery through resistance 73?. Relay 5% operated, closes a circuit from ground through the lower winding of relay M8, conductor 553, the upper back contact of relay M3, the upper outer front contact of relay 596', resistance 5l5, conductor 456 to battery through the upper winding of relay 4l8. Relay 5960perated, also grounds the sleeve of the selector SI over a circuit previously described, connects the tip and ring of thetrunk to the talk jack as previously described, opens its lower outer back contact, thereby preventing the operation of relays ii5, E29 and 62?, opens the operating path for relay M58 as previously described, and opens the operating paths for relays 639, M6 and 126.

In the dialing operationthe attendant dials the desired number by means of dial 566, and the dial pulses cause relay M8 to operate, and the circuit functions in the manner outlined heretofore and supplies the corrected alternating cu. rent dial pulses to the distant private branch ex change. When dialing is completed, the attendant removes the plug 565 from the dial jack 589. Relays 513 and M2 release but relay M8 remains operated under control of relay 5%.

Called party answers When the called party answers, a pulse of al ternating current is connected to conductors 6'10 and 61! as previously described and causes relay 6I5 to operate. Operation of relay tit: furnishes a ground through its right front contact which causes relays 4| l and 420 to function in the manner outlined heretofore in completing a call from a subscriber at substation A. Relay 4! l in operating connects the upper low resistance winding of relay 52 1 in series with resistance #26 across the tip and ring conductors of the trunkto give the attendant an answering supervisory signal. The circuit may be traced from tip conductor of talking jack 543, contact 591 of relay 5%, conductor 463, upper back contact of relay 528, con

ductor 432, upper left winding of coiltlld, conductor 429, upper front contact of relay ill, conductor 450, contact 595, conductor i6l, resistance 426, upper winding of relay 42%, conductor 430,1ower left winding of coil 55 3, conductor 433, back contact of relay 423, conductor Q64, innermost upper front contact of relay 555 to the ring of jack 543. Direct current flowing over this circuit from the'attendants cord 53 gives her a signal in a well-known manner that the called party has answered.

Release of the connection leases relay 418, and the circuit functions in the manner described heretofore in the completion of a call from a subscriber at substation A.

Incoming call Assume that it is desired to make a ,call from the line AI in a distant exchange, such as P. B. X. 2 to a line, such as line B, in P. B. l. Referring to Figs. 2 and 3, such a connection is extended by way of line finder LFl, selector S3, trunk T, selector S2, and connector C. When the trunk circuit T is seized by the distant P. B. X. 2, a pulse of alternating current is received over conductors 6'56 and 6' (Fig. 6) and is rectified by copper oxide rectifiers 6H), 6H, 6|2 and 6L3 in a manner well known to the art. This rectified current operates relay (H5 in the manner previously described. Relay 6E5 operated, completes a circuit from ground through theright front contact of relay 5l5 over conductor 546, the upper back contact of relay 1'26, conductor M5, the upper inner back contact of relay 529, conductor 736, the upper back contact of relay H5 to battery through the windingofrelay Hi6. Relay H8 operated, connects ground to the sleeve terminal M of the selector Si as a busy condition over a circuit extending from ground, through the upper middle front contact of relay N8, the upper back contact of relay 76H, conductor 439 to the sleeve terminal 4H] of the selector SI Relay H8 locks in a circuit extending from battery through the Winding of relay H8, the upper back contact of relay 7 I6 to ground through the upper inner front contact of relay H8. Relay H8 operated establishes a circuit from the upper outer armature of relay H over conductor 438, through resistance 426, the upper winding of relay 424, conductor Q36, the lower left winding of repeating coil 66% to the ring conductor 433 of the trunk circuit, the upper inner back contact of relay 428, conductor 155, the upper inner back contact of relay 596 to the ring terminal of the selector S2. A circuit is also closed from the upper outer front contact of relay llii over conductor 429, through the upper left winding of repeating coil 6M, tip conductor 432, the upper outer back contact of relay 528, conductor Q63, contact 596 of relay 590 to the tip conductor of the incoming selector S2. Thus the upper winding of relay 424 is connected in series with resistance 426 and the left windings of the 8' r repeating coil'604 and across the tipand the ring conductors of the incoming selector S2. Opera ation of relay 7 [8. also closes a circuit from ground lower front contact of relay H 8, through the lower inner back contact of relay ll-*8, over con- 7 ductor 452, lower back contact of relay 4l9, conductor 455, thereby short-circuitin'g the winding of relays 590 and 5l3.' The operating circuit of relay 590 was previously traced from battery through resistance HT and the lower outer back contact of relay ll'fi to conductor 452. This pre- 7 vents the operation of relays 509 and 5&3 thereby preventing mutilation of a call if an operator at P. B. X. I plugs into the jack 509-or 543 over a I busy test. At the termination of the alternating' current pulse, relay 615 releases.- Relay ms: operated, holds the upper winding of relay 424- in series with resistances H2 and 425 in series with the left windings of repeatingcoil 604 and the pulsing contacts of relays H15 and- 6'26 across the tip and the'ring conductors of the incoming selector S2. This circuit includes the loop from conductor 429 through the upper middle front contact of relay 103, the upper outer front contact of relay 105, in parallel with the circuit through the lower back contact of relay 526 con'ipleted over conductors T54 and 155 through the upper inner front contact of relay Hi3 and resistance H2 in addition to the loop circuit previously traced through the upper wi=ndingof relay 424 and resistance 426. Relay T93 operated also establishes a circuit from battery through the windingof relay 628, over conductor 135, through the upper outer front contact of r'elayl'03; over conductor 152' to the lower outer front contact of relay 623 for supervisory purposes. operated, opens its lower back contact thereby opening the circuit previously traded for' the operation of relay 428'. A circuit is also closed from ground through contact 174 of relay H5,

over conductor 45-! to battery through the wi-nding of relay 545, thereby causing relay 545 170 opcrate and apply a busy ground to the sleeve terminal of jack 543 and to apply a battery through resistance 54'! to ground, through lamp 5 48"causing lamp 548 tolight as a busy signal to the attendant. Operation of relay H5 also closes a tone circuit from ground, through the left wind ing of transformer 13!, through condenser 1311', through contact H of relay H to the upper inner front contact of relay Til-f which then leads over conductor 434 to the ring conductor of the outgoing trunk circuit. This tone: is furnished by the interrupter 133 which makes and breaks through the winding of relay H9.

Relay 1 l5 places relay 1B4 under-control ofrelays H and .When: the incoming selector S2 functions, ground is connected over the sleeve of the incoming selector S2, conductor 589 to the battery Relay H9 operated, causes the operation of relays 726 and HE and-holds relays H5, 129 and W3 operated. The operating circuit for relays 128 and lit extends from' ground on the right back contact of relay 6l5 over conductor 14?, through the upper inner front contact of relay H9, conductor 45%, the lower inner back contact of relay 428, conductor 465, contact 592 of relay 598, conductor 5121 to battery through the windings of relays 1 l6 and 126-. The holding ground for relays H5, 125 and I03 extends from the lower front contact of relay" ll-9, over conductor 51%, through the lower outer-back contact of relay 5953 to conductor 4'66 and thence to the windings of relays 1-29,- TI 5 and T53 over circuits previouslyrtraced. Relays T26 and 716 operated, lock under control of relay 129', over circuits extending from ground, through the lower front contact of relay 725, the lower front contact of relay 126' to battery through the winding of relay 1-25 and to battery through the winding of relay H6. Relay l26 operated connects the front contact of relay 5|5 to the winding of relay 530 in a circuit extending from the front contact of relay 6! 5, over conductor 146', through the upper front contact of relay 1Z6, conductor 518, contact 59! of relay 590, conductor 575 to battery throughthe winding of relay 630 for pulsing. Relay 7 it operated, opens the operating circuit previously traced for relay H8 and opens the operating path of relay 590'. Relay 'HS operated, also removes ground from the resistance H? to prevent current drain and provides'a holding path for relay 545 in a V circuit extending from ground, through the upper front contact of relay H6 to conductor 45! and thence to the winding of relay 545. Relay 5:45 closes another holding path through relay Relay 615 follows the alternating current pulses from the distant'P. B. X. 2 and inturn causes the relay 63D to pulse over a circuit previously described; Relay 630 operates on the first pulse of relays-l5 and opens the short circuit around relay I05- permitting relay 705 to operate in a circuit extending from battery through the winding of relay 194', resistance H0, lower front c'ontact'of relay 104, the winding of relay 105, the upper back contact of relay 122 to ground supplied to conductor 'I5l from the upper inner front contact of relay. 6-21. The resistance 12'! and; the condenser 728- are bridged around relay 63 Bin order to aid in pulsing. The relaylt4' remains locked in the operated position. Relay 1G5 opera-tedremoves the ground supplied to the upper armature of relay 638" over the circuit previously described, closes acircuit from ground 'on. the upper inner front contact of relay 105 to battery through the lower Winding of relay. 106' which opposes the upper winding of relay'lflii causing relay Hit to release, and removes the ground from the biasing circuit which has previously been traced through the lower winding of relay 122. When off-normal ground through the lower back contact of relay 1051s removed from the upper winding of relay I22, condenser I63 which has been discharged by this ground now charges in a circuit from battery through the'upper winding of relay I22 to ground through condenser I63 and resistance I62. Current will continue to flow through the upper winding of relay I22 during the charging of condenser I63 and the ampere turns produced by the charging current in the upper winding of relay I22 oppose the ampere turns in the lower winding of relay I22. As the condenser I63 becomes charged, the ampere turns in the upper winding of relay I22 decrease and the relay I22 is caused to operate by the ampere turns in the lower winding of relayl22 in a manner well known to the art. Relay I05 operated also causes relay I20 to operate inacircuit extending from the upper inner front contact of relay 621, conductor I5I, the lower front contact of relay I05, the winding of relay I20 and resistance I2l in parallel, to battery through re- 1 sistance I25. Relay I20'operated, opens the cirthereby permitting relay 606 to release.

cuit through the lower back contact of relay 120 to resistance III thereby removing the shunting resistance II I from around the winding of relay I05. When relay I06 releases, the upper front contact of relay I06 is opened and the short circuit around the Winding of relay II is removed. Relay I0I operates in a circuit extending from ground on the upper inner front contact of relay 621, conductor 15!, winding of relay 101, to battery through resistance I09. Closure of the upper backcontact of relay I06 establishes a circuit from ground on the upper inner front contact of relay 621, conductor Il, the upper back contact of relay I06, conductor I56, lower front contact of relay 621, to battery through the winding of relay 626. Relay 626 operates. Operation of relay I01 opens the circuit through the upper winding of relay I24. Relay I24 remains operated in a circuit from battery through its lower winding and its lower front contact in parallel with resistance I25 and in series with the winding of relay I20 and resistance I2l to ground on the upper inner front'contact of relay 62! over the circuit previously traced. Relay I0I operated, also opens the circuit previously traced from off-normal ground on the upper inner front contact of relay 621, to the winding of relay 60| Relay I01 operated, also closes a circuit from off-normal ground on the upper inner front contact of relay 621, conductor 15!, the upper front contact of relay I0I, contact I13 of relay H5, conductor I34, to battery through the winding of relay 60 l Relay 60l operated, causes relay 425 to operate over a circuit previously described. Relay 60l operated, also short-circuits the upper left and the lower left windings of repeating coil 604 and connects resistance 602. and condenser 603 across the pulsing loop to the incoming selector S2 in order to improve the pulsing. Relay 425 operated, performs no function atthis time.

When the relay I22 operates, it opens its upper back contact andthus opens the holding circuit previously described for relays I04 and I05 permitting these relays to release. Relay I04 released, short-circuits resistance H0 through the lower back contact of relay I04 sothat relay I04 operates quickly when its operating circuit is reclosed. Relay I05 released, reconnects the ground'on the upper back contact of relay I05 to the upper armature of relay 630 over a circuit previously described, and removes the ground from the lower winding of relay I06. This ground has previously discharged condenser I60.

Now when the ground is removed condenser I60 charges in a circuit from battery through the lower winding of relay I06 to ground through condenser I60 and resistance I6l. Current will continue to flow through the lower winding of relay I06 during the charging of condenser I60 and the ampere turns produced by the charging current in the lower winding of relay F06 opposes the ampere turns in the upper winding of relay I06. As the condenser I60 becomes charged the ampere turns in the lower winding of relay 106 decrease and the relay I06 is caused to operate by the ampere turns in the upper winding of relay I06 in a manner well known to the art. Relay I05 released, also opens the holding circuit previously described for relays I20 and I24, and the bridge across the tip and ring conductors of the incoming selector S2 as previously described since relay 626 is now operated. The relay I20 released closes a circuit from ground on the upper inner front contact of relay 62I over conductor I51, the lower back contact of relay I20, resistances Ill and H0 to battery through the winding of relay I04. Relay I04 does not energize sufiiciently to operate but only sufficiently to cause relay I04 to operate quicklywhen relay 630 is released on the next dial pulse. Relay I20 released, also closes a circuit from ground ontheupper inner front contact of relay 621 over conductor I5 I, the lower back contact of relay I05, the upper back contact of relay I20 to battery through the upper winding of relay I22 causing relay'122 to release in amanner well known to the art and close its back contact. When the bridge across the tip and the ring conductors of the incoming selector S2 is opened by the release of relay I05 the incoming selector S2 will step.

Let us assume that the dial used at the distant P. B. X. 2 has a speed in excess of the average. Relay 630 releases, reoperating relay I04 in the circuit previously traced. Relay 630 reoperates in the succeeding operation of relay 6 l5, permitting relay I05 to reoperate in the circuit previously described. Relay I05 operated closes the circuit through the lower winding of relay I06 before the upper winding of relay I06 is energized thereby preventing the operation of relay I06. Relay I05 operated also closes the loop circuit previously described to the incoming selector S2, terminating the previous pulse. Thus: on high dial speeds the period between pulses during which the circuit to the incoming selector S2 is closed is determined by the operating time of the relay I22 plus the release time of the relay I05 regardless of the per cent break of the pulses received.

Let us assume that .the dial used at the distant P. B. X. 2 has a speed less than the average. Relay 630 releases on the succeeding open period of the pulse and reoperates relay I04 in the circuit previously traced. Before relay 630 reoperates on the succeeding pulse relay I06 operates in a circuit through the upper winding of relayi06 as previously described. Operation of relay I06 opens the holding circuit previously de-. scribed for relay 626 permitting relay 626 to release and release the relay 620 which in turn releases and closes the loop to the incoming selector S2 causing a pulse. Thus, on slow dial speeds, the period between pulses during which the circuit to the incoming selector S2 is opened is determined by the operate time of relay I06 plus the release time of relay 626 regardless of the percentage break of the pulses received. The relay I06- operated also short-circuits the winding of relay 161 which is slow in releasing but relay Hi6 reoperates onthe next 'puls'e before relay Hll'has time to release. 2

On single pulse digits or the last pulse ofother circuit to the incoming selector S2 is opened is the same as on slow dial speeds regardless of the speed of the pulsing received. In this case, the relay H36 operated, short-circuits the winding of relay l6! causing relay in! to release and in turn operate the relays 666 and E24 over circuits previously described and release the relay 66!. Relay Bill released removes the short-circuits from'the left windings of repeating coil 604, re-

leases relay 425 and closes through the transmission circuit. Relay 666 operated removes the" short-circuits'from the telephone repeater 666. Relay E24 operated short circuits the resistance 123. The relay 124- being operated during the operating time of the relay 122 on the first pulse of each digit increase's'the current in the lower winding of relay l22,'therebyi making relay "722 faster to operate so as to compensate forl the fact that the relays delivering pulses to this cir cuit are slower to release on the first pulse of 'a digit than onsucceedingpulses. v

Called party answers When the pulsing'is completed andthe called party answers, battery and ground are reversed in the connector C in a manner well known to the art. 424 to opf rate over the loop circuit previously described. Operation of relay 424 operates'relay 423 in a circuit from ground through'the lower front contact of relay 424 to battery'through: the

612 and 613 to the'tip conductor 61 0 and the ring conductor (ill of the line to the distant P. B. X. 2, to reduce the amount of induction in other lines and operates relay 601 which in turn operates relay 425 over circuits'previously described. Relay 623 operated sends a pulse of alternating current as a supervisory signal to the calling party in the manner previously described, and establishes a circuit from ground through the lower outer front contact of relay 623 over conductor 152, the upper outer front contact of relay i63 conductor 738 to battery through the wind ing of relay 628. Relays 623 and 624 lock in a circuit extending fromground through contact TH of relay H5, conductor 753, the lower middle front contact of relay 623, the upper outer back contact of relay 629,, windings of relays 623 and 624' in paralleLto battery through the lower back contact of relay 636. 'After an interval relay 628 operates and operates relay 629 from ground through the lower front contact of relay 628.

Operation of relay 628 also closes a circuitfrom ground on the lower front contact of relay l03, conductorl45, the upper front contact of relay 628, conductor 431, winding of relay 420 to bat tery through resistance 422 thereby energizing relay 42ll. Operation of relay 629 releases relays 623and 624 andholds relay 426 which locks, to

ground supplied over conductor 451 from con- Thisreversal causes polarized relay described heretofore.

tact 114 of relay H5 and from the upper front contact. of relay H6. When relays 623'and 624 release, the alternating current is disconnected 1 from conductors 676 and fill of the line to the 7 digits, the period of the pulse during which'the' calling P. B. X. 2, the'transmission' circuit is closed and relays 66!, 425, 628 and 629'release. When relay 629 releases relay 4!! operates over the circuit previously described but performs no function at this time. The circuit is now ready for talking. a

Release of connection If the called party B disconnects first, battery and ground are reversed in theconnector C, and, since relay 424 is a polarizedrelay, it releases and in turn releases relay 423. Relays 423 and 424 released, operate relays 623 and 624 undercontrol of relays 426 and 629 over circuits previously traced. Relay 623 operated connects the source of alternating current to the calling P. B. X. 2 in the manner described heretofore, locks independently of relays 423 and 424 to ground on contact TH of'relay H5, over acircuit previously described, and closes the operating circuit previously, described for relay 628. Relay 628-operated, in turn operates relay 629 as previously described. Relay 629 operated releases relays 623, 624ar1d423. Relay 623 released, terminates the pulse. of alternating current to the calling P. B. X. 2, and releases relay 628 which in turn releases relays 623 and 4! I. .If the called party B comes in on the connection again before the calling P. B. X. 2 disconnects, relays 424 and 423 reoperate and the circuit functions in the manner If the called end flashes, the circuit is so arranged'that no matter how fast the flashing, a disconnect signal will not be given to the calling 'P. B. X. 2.

If the calling .end disconnects first, a pulse of alternating current is received from .the calling Relay 645 operates the operating battery from relay 623 preventing operation of relay 623 if the originating end disconnects before the calling end. When the short circuit is removed from relay H35 by the operation of relay 636 the relay T05 operates in series with resistance 1 l6 and the winding of relay 104 over the circuit previously traced. Relay I05 operatecl, releases relay 106 by applying ground to the lower winding of relay H16, operates relays F26 and 122 in the manner previously described herein, and holds the loop to the called end closed. When the relay. 1B6 releases, the relays 626 and llll operate over circuits describedheretofore. Relay lll'l operated releases relay666 and operates relay 66! which in turn operates relay 425.

When relay ":22 operates, relays 164 and (05 release Relay 627 now, holds under control of relay 6M to ground on the left inner front contact of relay 56!. Relay 705 released, opens the loop to the called end, releases relays I22 and and again permits relay 106 to operate in the manner described heretofore. If relay 424 is oper ated when the calling end disconnects, relay 424 releases when the loop to the called station B is opened. However, release of relay 424 is ineffective since the operating battery for relays 623 and 624is still held open by relay 630. The resistance 72! is connected in parallel with relay 526 to make relay F26 slow to release to insure the release of relay 104 before relay 122 releases;

Relay 766 operated, releases relay 101 which in turn operates relay 606 overa circuit previously described, and releases relay 60! which in turn releases relay 425. When. the incoming selector S2 releases, ground is removed from the sleeve releasing relay H9. Relay H9 released, releases relays H13, H 5 and 129. When relay 129 releases the relays 726 and H6 remain operated under control of relay 515 over a circuit, previously traced. At the end of the disconnect signal, relay 615 releases, in turn releasing relays 126, H B and 639. Relay H5 released, releases relay 545. Relay 545 released, releases relay 621 which in turn releases relays Hi6 and 696, and removes ground from the sleeve terminal M of the outgoing selector Sl thereby restoring the circuit to normal.

Flashing supervision A detailed description will now be given of the operation of the system when a called station flashes his switch-hook for the purpose of securing the attention of an attendant operator. In order that this feature of the invention may be more clearly understood, those parts of the detailed circuits necessary for its disclosure have been included in the diagram of Figs. 2 and 3.

With reference, therefore, to these figures assume that a connection has been extended from a station in exchange P. B. X. I by way of the attendant operators cord circuit 534 over the trunk T to the exchange P. B. X. '2 and thence through selector S4 and connector CI to a called station BI. Assume also that, after the connection has been fully established in'the manner already described in detail, the party at station Bl wishes to attract the attention of the operator and that he flashes his switch-hook. While the called partys receiver is off the switch-hook,

supervisory relay 324 and relay 323 are in an operated condition, the relay 324 receiving current from battery at the connector switch CI. Also, relays 3H and 32B are operated. Upon the first opening of the loop at the called station when the called party begins to flash his switch-hook, the called line supervisory relay 33B releases and current is reversed in the connector switch CI in the well-known manner and the polarized supervisory relay 324 releases, in turn releasing relay 323. The release of relay 324 causes the opera- 5 tion of relay 325 to send a signal of alternating current as a disconnect signal from the source 3!? over the trunk to the originating end. The circuit of relay 325 extends from the grounded contact of relay 324, front contact of relay 320,

% conductor 351, back contact of relay 6% to the winding of relay 325. The operation of relay s25 closes an energizing circuit for relay 628, WhlCh in turn closes an operating circuit for relay 629.

' Relay G26 closes a circuit from ground through its right-hand armature, thence through the front contact of relay 3 and resistance 322 to battery. This shunts relay 320 which thereupon releases. Relay 3 continues to hold in a circuit from battery, through resistance 32l, winding of relay 3! I, normal contact of relay 320, conductor 35!) to ground at the contact of relay 628 and later to ground at the contact of relay 629. Relay 629, which is slow to operate and slow to release, operates after an interval and opens the circuit of relay 325, which releases and removes the alternating current from the trunk. Relay 325 in turn opens the circuit of relay 628, which releases after an interval and brings about the release of relay 629 after a further interval. When ground is removed, from conductor 35!], relay 3| l releases.

On the next closure ofthe loop at the called station, supervisory relay 330 reoperates to reverse the direction of current, and relays 324 and 323 again operate. Relay 323 completes a circuit from ground throughits front contact, upper back contact of relay 326, conductor 35L left contact of relay 629 through the winding of relay 325 to battery. Relay 325 operates and applies alternating currentto the line to indicate that the called subscribers receiver is off the hook. Relays 528 and 62.9 again operate. When ground is applied to conductor 359, relay 326 operates in a circuit extending from said conductor through the normal contact of relay 329, winding of said relay, resistance 322 to battery. Relay 320 operates and locks to its own grounded contact. Relay 326 in operating opens the circuit of relay 325, which releases and removes the alternating current impulse from the line. Relay 325 also causes the release of relays 628 and 629. When ground is removed from conductor 359, a shunt is removed from the winding of relay 3| l, and this relay now operates over a circuit leading to ground through the operated contact of relay 320.

This procedure continues so long as the called party does not open and close his switch-hook contacts faster than the rate at which the relays are designed to transmit the alternating current impulses over the trunk. In practice, however, the called party is likely to operate his switchhook at a rate greater than the pulsing rate of the relays. And, unless some provision were made the last alternating current impulse transmitted when the called'party had finished operating his switch-hook might or might not represent the condition in which the called party leaves the switch-hook after his flashing operation. That is to say, he may leave the receiver off the hook following flashing or he may hang it up. Obviously it is necessary that the last signal impulse of alternating current should represent the condition of the switch-hook at that time in order that the equipment at the originating ofiice may so operate as to advise the operator of the exact condition of the called partys switch-hook.

In order that this requirement may be met, the

circuits are so designed that the alternating current pulses are sent at the same rate as the flashing of the called partys switch-hook until the rate of the switch-hook flashing exceeds that of the impulse transmitting relays, and thereafter alternating current impulses are transmitted at the rate for which the controlling relays are designed. But the transmitting relays in every case test the condition of the called partys switchhook before transmitting the alternating current impulse. For example, if the last alternating current impulse transmitted represented the closed condition of the called partys loop, when the relays are ready to transmit the next alternating current impulse representing the open condition of the loop, a test is first made to determine whether the loop is in the open or closed condition. If, at that instant, it is in a closed condition no impulse will be sent until the loop is found to be in an open condition. Then an alternating current impulse is sent representing the open condition of the called partys loop. In this way each alternating current impulse representsthe exact condition of the called partys loop at the time it is sent regardless of how many times the loop may be opened and closed by the. 75-

switch-hook between the transmission of successive alternating current impulses. V

An analysis of'the circuits will show that the test for the condition of the called partys loop is made alternately at'the front and back contacts of supervisory relaytz i, which is contro led by said loop. If the loop is in a closed condition,

relays 324 and 323 are energized; also, switching relays 32d and 3!! are energized, and relay 325 after having sent the last pulse is now released.

7 Should the loop be opened suddenly following its last closure, relay 3% would release and close a circuit from ground through the front contact of operating relay 32% to conductor 35L a suflicient interval elapsed between the last closure of the loop and the next opening, the timing relay 629 would have released, and the circuit by way of conductor 35l would now be completed to the relay 525. However, since the loop was opened suddenly following its closure, relay 525 does not have time in which to release, and, therefore, the release of relay 32d does not cause the immediate reoperation of relay 325. If the loop,.

a signal representing the open condition of the' loop until relay 629 has released and the loop is again opened following the release of said relay 629. When this occurs, relay 325 operates and transmits the impulse to theoriginating end.

Likewise, relay 325 having operated to transmit an impulse representing the open condition of the loop, this relay cannot again be operated to transmit a closed loop signal until relay 625 has measured its full interval and the loop is brought to a closed condition thereafter.

Therefore, no matter how rapidly the switchhook flashed, the signal impulses are sent to the originating end in an orderly manner, representing alternately the open and closed condition of the called station loop. And, when the party at the called station finally ceases flashing the switch-hook, the last pulse to be sent to. the originating end will definitely represent the condition in which the switch-hook is left.

Referring now to the originating exchange P. B. X l, the effect of these supervisoryimpulses on the operators supervisory lamp 59! will now be briefly described. Each alternating current impulse transmitted over the trunk T operates the relay M5 in the manner fully described hereinbefore. Assuming that an impulse representing a closure of the called partys loopis transmitted, relay 615 operates and closes a circuit from ground through its armature, normal contact and winding of relay 32h, resistance 22 to battery. Relay 42! operates and looks through its front contact. Relay 42c completes a circuit from battery, through resistance 42!, relay ll! to ground through the front contact of relay 4-26. Relay 4, however, is' shunted by a circuit from battery, through resistance 42! and back contact of relay til to ground at the armature of relay M5. When relay EH5 releases at the end of the impulse, the shunt is removed and relay 4H operates. Relay All bridgesthe "relay 424 across the tip and ring conductors of closed contacts of relay 420 to ground at the contact of relay 515. Atthe end of the alternating current impulse relay 5E5 again releases and the circuit of relay 4H is opened. Relay ii i opensthe bridgeacross the tip and ring conductorsa nd the operators supervisory lamp 5!!! lights .to indicate that the called loop is opened.

"Tmfiic' registration .On either an incoming call from a distant P. B. X. 2 or an outgoing call to a distant P. B. X. 2, relay 565 operates-thereby opening one of the multiple paths'of the traffic register circuit over conductor 5&5. When all the tie lines ina particular group are busy, all the relays 545 in the various tie lines operate and the ground circuit to the traiflc register is opened, thereby. causing a registration. I

. Seizure without sub-sequent dialing If relay Bl5 operates falsely due to surges or if relay 6i 5 operates-0n an incoming call and if no dialing follows the seizure, the tie line will automatically time out in the following manner.

When the circuit'is seized the various relays and. equipment function in the manner previously described under seizure on an incoming call. When the incoming selectorSZ is seized, ground is connected from the incoming selector S2 to conductors 58!] and 58! in a manner well known to the art. If no dialing occurs, conductor 581 remains'grouhded and battery on conductor H3 is supplied from a timing circuit in a manner well known to the art through the lower winding of relay 882 to the ground on conductor 58!. Relay l'ElZ operates and locks to battery through the lower inner front contact of relay 702. After an interval, ground is supplied from the timing circuit over conductor H4 and is extended through the lower outer front contact of relay 702, the upper front contact of relay 126, conductor 578, contact 59! of relay 5%, conductor 515, to battery through the winding of relay 63h. Operation of relay 63!] causes the circuit to function as described heretofore under disconnection. Relay 102 looks in a circuit from ground through the upper winding of relay 162, the upper front contact of relay 702, conductor M2 to battery through the lower front contact of relay 636. After an interval, ground is removed from conductor 'il l thereby permitting the circuit to restore to normal.

What is claimed is:

,1. In a telephone system. a distant oifice, a trunk line leading to said distant'ofiice, an in pulse repeater having an input. circuit and an outputcircuit, a relay in said input circuit for causing repeated impulses to be produced in said output circuit, two circuit branches for said trunk for extending outgoing callsover the trunk to the distant oflice, means for producing impulses representative of a call in either of said branches, a relay for delivering the impulses for either branch to the relay in said input circuit, and means for delivering the impulses produced in said output circuit to said trunk.

2. In a telephone system, a distant oflice, a trunk line leading to said distant ofiice, an impulse repeater having an input circuit and an output circuit, a relay. in saidinput circuit for causing repeated impulses to be produced in said output circuit, a branch for said trunk over which calls are extended by automatic switches, a second branch for said trunk over which calls are extended by an operator, means for producing impulses in either of said branches, a relay for delivering the impulses for either branch to the relay in said input circuit, and means for'delivering the impulses produced in said output circuit to said trunk.

3. In a telephone system, a trunk line extending to a distant point, an impulse repeater having an input circuit and an output circuit, two circuit branches for said trunk for extending outgoing calls over the trunk to the distant point,

means for producing impulses representative of 'a call in either of said branches, and a single impulse relay common to both branches and serving to deliver to the input circuit of said repeater impulses produced in either of said branches.

4. In a telephone system, a two-way trunk having two branches at one end thereof, an impulse repeater having an input circuit and an output circuit, means for producing impulses representative of a call in either of said branches, means for delivering impulses for either branch to the input circuit of said repeater, means for delivering the impulses in the output circuit of said repeater to said trunk on an outgoing call, and means to deliver impulses incoming over said trunk to said input circuit.

5. In a telephone system, .a distant ofiice, a two-way trunk extending to said distant office, a first branch for said trunk for originating calls outgoing over the trunk, a second branch for receiving calls incoming over said trunk, an impulse repeater having an input circuit and an output circuit, and means for delivering the impulses from either said first branch or from said trunk to said input circuit and for delivering the impulses in said output circuit either to said trunk or to said second branch according to the direction of the call.

6. In combination, a repeater having an input circuit and an output circuit, means for sending either direct current or alternating current impulses toward said repeater, means in said input circuit operable in accordance with either said direct current or said alternating current impulses, and means responsive to the impulses produced in said output circuit for sendingeither alternating current or direct current impulses away from said repeater.

7. In combination, a repeater having an input circuit and an output circuit, means for sending alternating current impulses, means for converting said alternating current impulses into direct current impulses and for delivering said direct current impulses to the input circuit of said repeater, means for transmitting direct current impulses and for delivering them to the input circuit of said repeater, means for producing direct current impulses in the output circuit of said repeater, and means for converting said latter impulses into impulses of alternating current.

8. In combination, an impulse repeater having an input circuit and an output circuit, means for sending either direct current or alternating current impulses toward said repeater, means in said input circuit operable either in accordance with said direct current or said alternating current impulses, means for producing corrected impulses in the output circuit of said repeater, and means responsive to said corrected impulses for sending either alternating current or direct current impulses.

9. In combination, an impulse repeater having an input and an output circuit, a trunk line over which impulses may be sent in either direction, means for switching said input circuit so as to receive impulses coming in either direction over said trunk and for switching said output circuit so as to send out impulses in either direction, and means for correcting the impulses received by the input circuit regardless of the direction of transmission oversaid trunk.

10. The combination with an impulse repeater having an input circuit and an output circuit of a trunk line over which impulses may be sent in either direction, means for switching said input circuit so as to receive impulses coming in either direction over said trunk and for switching said output circuit so as to send out impulses-in either direction, and means efiective if the speed of impulse transmission is too high or too low for correcting the impulses received by the input circuit.

11. In a telephone system, a trunk leading to adistant point, two branches for said trunk for originating outgoing calls, means for sending signaling currents over said trunk from the distant point, means for converting said currents: into supervisory signals of one character if the call originated in one of said branches, and means for converting said currents into supervisory signals of adifferent character if the call originated in the other of said branches.

12. In a telephone system, a trunk line extending to a distant oflice, two branches for said trunk for originating outgoing calls, means for sending signals of alternating current over said trunk from the distant oifice, means for converting said alternating currents into direct current supervisory signals of reverse polarity if the call originated in one of said branches, and means for converting said alternating currents into open and closed circuit direct current supervisory signals if the call originated in the other of said branches.

13. The combination with an incoming circuit and an outgoing circuit of means for sending signals over said incoming circuit at a given rate, means operable while said incoming signals are being sent for sending signals over said outgoing circuit at a different rate, and means for making a test to determine the condition of said incoming circuit prior to the sending of an outgoing signal.

14. The combination with an incoming circuit and an outgoing circuit of means for sending signals over said incoming circuit at a given frequency, means responsive to the incoming signals for sending signals over said outgoing circuit at a difierent frequency, and means for making a test to determine the condition of the incoming circuit before each outgoing signal is sent.

15. The combination with an incoming circuit and an outgoing circuit of means for producing signals in said incoming circuit at a given frequency, means operable while said signals are being produced in said incoming circuit for sendent frequency, and means for making a test of the incoming circuit before each outgoing signal is sent to'determine if the incoming circuit has changed its condition since the last outgoing signal was sent.

16. In a signaling system, an incoming circuit I and an outgoing circuit, means for sending signals over the incoming circuit at a given frequency, a transmitting device, and means responsive to said incoming signals for operating said device at a frequency diiferingfrom that of said incoming signals to send on each operation thereof a signal over said outgoing circuit,

and means for rendering each operation of said' transmitting device dependent on a change in the condition of said incoming circuit.

17. In a signaling system, an incoming circuit device dependent on a change in the condition of said incoming circuit as compared with the condition existing on the precedingoperation of said device.

18. In a signaling system, an incoming line and an outgoing line, means for producing signals in said'incoming line at agiven rate, and means operable while said signals are being produced in said incoming line for sending over the outgoing line a series of signals at a different rate and for synchronizing each outgoing signal with an incoming signal. 7

19. In a signaling system, an incoming line and an outgoing line, means for sending over said incoming line a variable number of signals comprising signals of one character occurring in alternate succession withsignals of a second character, and means operable during the interval said signals are being sent for sending over said outgoing line a difierent number of successive signals and for synchronizing the outgoing'signals with incoming signals of both characters;

20. The combination'with' an incoming circuit and an outgoing circuit of means for sending signals over said incoming circuit at varying rates, and means for sending over said outgoing circuit signals in synchronism With said incoming signals provided the rate of the incoming signals remains on one side of a limiting value, for sending said outgoing signals at a fixed rate if the rate of the incomingsignals passes to the other side of said limiting value, and for synchronizing the sending of each outgoing signal with one of the incoming signals.

21. The combination in a signaling system of an incoming circuit and an outgoing circuit,

means for sending over said incoming circuit sig nals of varying duration and at varying frequencies, and means operable while said incoming ing signals over said outgoing circuit at a differsignals are being sentfor sending over said outgoing circuit signals of fixed duration and of a frequency corresponding to the frequency of the incoming signals only if the frequency of said incoming signals is within certain limits and'for synchronizing the sending of each outgoing signal with one of the incoming signals.

22. The combinationin a signaling system of an incoming signaling circuit having a signal receiving relay therein, switch-hook means for controlling said circuit to send signals to said relay,

an outgoing signaling circuit, a source of current.

for sending signals of different character over said outgoing circuit While said relay is operating 7 in response to said incoming signals, a transmitting relay for applying said source to said outgoing circuit, a circuit for operating said transmitting relay, and means for directing said circuit alternately to a front contact and to" a back contact of said signal receiving relay to test the condition of said signal receiving relay before transmission of each outgoing signal.

23. In a signaling system, an incoming line and an outgoing line, means for sending a variable number of successive signals over said incoming line, and means operable during the interval said signals are being sent for sending over said 'outgoing line a different number of successive signals and for synchronizing each of the outgoing signals with one of the incoming signals.

24. In a signaling system, an incoming line and an outgoing line, means for sending a variable number of successive signals over said incoming line, and means operable during the interval said signals are being sent for sending-over said outgoing line a succession of signals'the number of which differs from the number of signals sent over the incoming line and varies according to the frequency of the signals sent over said incoming line. 1

25. In a signaling system, an incoming line and an outgoing line, means for sending over the incoming line a variable number of signals comprising signals of .one character occurring in alternate succession With signals of a second character, and means operable during the interval said signals are being sent for sending over said outgoing line a diiferent number of signals of the same character and for synchronizing said outgoing signals with incoming signals of both characters. V V

26. In a signaling system, an incoming line and an outgoing line, means for sending over the incoming line a variable number of signals comprising signals of one character occurring in alternate succession with signals of a second charactenand means operable during the interval said signals are being sent for sending over the outgoing'line a different number of successive signals all of like character, each outgoing signal being synchronized with an incoming signal of one character and the succeeding outgoing signal with an incoming signal of the other character.

JOHN BAUMEAIK. 

